Mercutio
Fatwah on Western Digital
Ages and ages ago, I had issues with Asus Pentium 4 motherboards having a hard-coded thermal shutdown limit that was set too low. Those systems didn't freeze. They'd go hard-off and then display a boot time message indicating that the CPU had experienced a thermal event.
You might want to look and see if there are system event messages in your BIOS that are being suppressed since you're not getting those sorts of boot-time errors and fan control seems to be a factor.
You might want to look and see if there are system event messages in your BIOS that are being suppressed since you're not getting those sorts of boot-time errors and fan control seems to be a factor.